Systemic immunity requires SnRK2.8-mediated nuclear import of NPR1 in arabidopsis

Abstract

In plants, necrotic lesions occur at the site of pathogen infection through the hypersensitive response, which is followedby induction of systemic acquired resistance (SAR) in distal tissues. Salicylic acid (SA) induces SAR by activatingNONEXPRESSER OF PATHOGENESIS-RELATED GENES1 (NPR1) through an oligomer-to-monomer reaction. However, SAbiosynthesis is elevated only slightly in distal tissues during SAR, implying that SA-mediated induction of SAR requiresadditional factors. Here, we demonstrated that SA-independent systemic signals induce a gene encoding SNF1-RELATEDPROTEIN KINASE 2.8 (SnRK2.8), which phosphorylates NPR1 during SAR. The SnRK2.8-mediated phosphorylation of NPR1 isnecessary for its nuclear import. Notably, although SnRK2.8 transcription and SnRK2.8 activation are independent of SAsignaling, the SnRK2.8-mediated induction of SAR requires SA. Together with the SA-mediated monomerization of NPR1,these observations indicate that SA signals and SnRK2.8-mediated phosphorylation coordinately function to activate NPR1via a dual-step process in developing systemic immunity in Arabidopsis thaliana. © American Society of Plant Biologists